Power hand tool

ABSTRACT

A power hand tool includes a housing, a motor mounted inside the housing, a transmission member coupled to the motor, a driven member, which has grooves on one side thereof facing the transmission member, a plurality of steel balls respectively mounted in the grooves of the driven member, a plurality of spring members respectively mounted in the transmission member and stopped at the steel balls for enabling the driven member to be rotated by the transmission member upon operation of the motor, and a tool bit adaptor fastened to the driven member. When the driven member receives a heavy reaction force through the tool bit adaptor, the steel balls can be disengaged from the grooves, thereby causing disconnection of the transmission member from the driven member so that the power hand tool runs idle to prevent

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to power hand tools and more specifically,to a power hand tool, which can prevent damage to the internaltransmission mechanism thereof and/or the fastener driven by the powerhand tool upon receiving a reaction overload.

2. Description of the Related Art

A conventional power hand tool mainly comprises a housing and a motormounted inside the housing. A bit adaptor is connected to an outputshaft of the motor for holding a bit, for example a screwdriver bit.When pressed the starting button of the power hand tool to start themotor, the output shaft is driven to rotate the bit adaptor and thescrewdriver bit held in the bit adaptor, thereby driving the screwengaged with the screwdriver bit into a workpiece, for example, acircuit board.

However, if the user does not release the starting button immediatelyafter the screw has been fully driven into the workpiece, the outputshaft will keep rotating the bit adaptor and the screwdriver bit againstthe screw at the workpiece. At this time, the screw or workpiece or theinternal transmission mechanism of the power hand tool may be damageddue to an overload. In order to prevent this problem, the user must keepadjusting the force pressed on the starting button so as to adjust theoutput torque of the power handle tool. Therefore, the use of this kindof power hand tool is inconvenient.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances inview. It is therefore one objective of the present invention to providea power hand tool, which can prevent damage to the internal transmissionmechanism, the workpiece or the fastener upon an overload.

To achieve this objective of the present invention, the power hand toolcomprises a housing having an accommodation chamber therein, a motormounted in the accommodation chamber, a transmission member mounted inthe accommodation chamber and coupled to the motor for rotation by themotor, a driven member mounted in the accommodation chamber and providedwith at least one groove on one side thereof facing the transmissionmember, at least one steel ball mounted in the at least one groove ofthe driven member, and at least one spring member mounted in thetransmission member and stopped at the steel ball, thereby enabling thedriven member to be rotated by the transmission member upon operation ofthe motor.

When the power hand tool receives a reaction overload, the steel ball isforced to disengage from the groove, thereby causing disconnection ofthe transmission member from the driven wheel such that the transmissionmember runs idle. Therefore, the power hand tool runs idle when receivesan overload, preventing damage to the internal transmission mechanismthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a power hand tool according to a preferredembodiment of the present invention.

FIG. 2 is a sectional view of the power hand tool according to thepreferred embodiment of the present invention, showing that the steelballs are engaged in the grooves of the driven member.

FIG. 3 is similar to FIG. 2, but showing that the driven member isrotated with an angle and the steel balls are forced to disengage fromthe grooves of the driven member.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, a power hand tool 10 in accordance with apreferred embodiment of the present invention comprises a housing 20, amotor 30, a transmission member 40, a driven member 50, a plurality ofsteel balls 60, a plurality of spring members 70, and a tool bit adaptor80.

The housing 20 is formed of two cover shells 22 abutted together,defining therein an accommodation chamber 24. Further, a starting button(not shown) is provided at the housing 20.

The motor 30 is mounted in the accommodation chamber 24 of the housing20 and electrically coupled to the starting button at the housing 20.The motor 30 has an output shaft 32 and a pinion 34 fixedly mounted onthe output shaft 32.

The transmission member 40 is mounted in the accommodation chamber 24 ofthe housing 20 and has a transmission gear 42 meshed with the pinion 34.The transmission gear 42 has a center axle hole 422 through the frontand back sides thereof, and a plurality of through holes 424equiangularly spaced around the center axle hole 422. The transmissionmember 40 further comprises a cover plate 44 attached to one side of thetransmission gear 42. The cover plate 44 has a through hole 442corresponding to the center axle hole 422 of the transmission gear 42.

The driven member 50 is mounted in the accommodation chamber 24 of thehousing 20 and has a driven wheel 52 and a driving shaft 54. The drivenwheel 52 has a center through hole 522 corresponding to the center axlehole 422 of the transmission gear 42, and a plurality of arched grooves53 formed on one side facing the transmission gear 42 and equiangularlyspaced around the center through hole 522. The arched groove 53 has afront end 532 and a rear end 534. The center through hole 522 of thedriven wheel 52 is a polygonal through hole. The driving shaft 54 has afront end 542, a rear end 544, and a shoulder 546 between the front end542 and the rear end 544. The shoulder 546 has a polygonal cross sectionfitting the polygonal through hole 522 of the driven wheel 52. The rearend 544 of the driving shaft 54 is inserted in proper order through thecenter through hole 522 of the driven wheel 52, the center axle hole 422of the transmission gear 42 and the through hole 442 of the cover plate44, and then a retainer 56 is fastened to the rear end 544 of thedriving shaft 54 to secure the driving shaft 54 to the transmissionmember 40. Further, a cushion ring 58 is mounted on the driving shaft 54and sandwiched between the cover plate 44 and the retainer 56.

The steel balls 60 are respectively mounted in the front end 532 of eachof the arched grooves 53 of the driven wheel 52 and partially projectingin the spring holes 424 of the transmission gear 42.

The spring members 70 are respectively mounted in the spring holes 424of the transmission gear 42 and stopped between the steel balls 60 andthe cover plate 44. The spring members 70 impart a pressure to the steelballs 40 against the inside wall of each arched groove 53 of the drivenwheel 52, thereby allowing synchronous rotation of the driven wheel 52and the driving shaft 54 with the transmission gear 42.

The tool bit adaptor 80 is fastened to the front end 542 of the drivingshaft 54 to hold, for example, a screwdriver bit for synchronousrotation with the driving shaft 54 to drive a screw (not shown) engagedwith the tool bit adaptor into or out of the workpiece.

Referring to FIG. 3, when the user keeps the starting button of thepower hand tool 10 pressed and started the motor 30, the motor 30 drivesthe transmission member 40 and the driven member 50 to rotate, causingsynchronous rotation of the tool bit adaptor 80 and the attachedscrewdriver bit, thereby driving the attached screw into the workpiece.If the user does not release the starting button of the power hand tool10 after the screw has been fully driven into the workpiece, the toolbit adaptor 80 may receive a heavy reaction load. At this time, a thrustforce from the driven wheel 52 against the steel balls 60 may surpassthe spring force imparted by the spring members 70 to the steel balls60, thereby causing the steel balls 60 to be forced by the driven wheel52 into the inside of the spring holes 424 and the driven wheel 52 willbe rotated relative to the transmission gear 42, such that thetransmission member 40 is separated from the driven wheel 52 to runidle. When the transmission member 40 runs idle, no more torque will betransmitted to the screw through the driven member 50 and the tool bitadaptor 80, thereby preventing the possible damage to the screw,workpiece or the transmission mechanism of the power tool.

As indicated above, the power hand tool 10 of the present inventionutilizes the spring members 70, the steel balls 60 and the archedgrooves 53 to have the transmission member 40 be disconnected from thedriven wheel 52 when the tool bit adaptor 80 receives an excessivereaction force, preventing damage to the parts of the power hand tool10.

Although a particular embodiment of the invention has been described indetail for purposes of illustration, various modifications andenhancements may be made without departing from the spirit and scope ofthe invention. Accordingly, the invention is not to be limited except asby the appended claims.

1. A power hand tool comprising: a housing having an accommodationchamber therein; a motor mounted in said accommodation chamber; atransmission member mounted in said accommodation chamber and coupled toand rotatable by said motor; a driven member mounted in saidaccommodation chamber, said driven member having at least one groove atone side thereof facing said transmission member; at least one steelball mounted in said at least one groove of said driven member; and atleast one spring member mounted in said transmission member and stoppedat said at least one steel ball to force the steel ball to stop againsta wall of said at least one groove of said driven member, therebyenabling said driven member to be rotated by said transmission member.2. The power hand tool as claimed in claim 1, further comprising a toolbit adaptor fastened to and rotatable by said driven member.
 3. Thepower hand tool as claimed in claim 1, wherein said transmission membercomprises a transmission gear having at least one spring hole and acover plate attached to said transmission gear; wherein said at leastone spring member is mounted in said at least one spring hole with twodistal ends thereof stopped against said at least one steel ball andsaid cover plate.
 4. The power hand tool as claimed in claim 3, whereinsaid driven member comprises a driven wheel having said at least onegroove, a driving shaft having an end fastened to said tool bit adaptorand the other end inserted through said driven wheel, said transmissiongear and said cover plate and coupled with a retainer.
 5. The power handtool as claimed in claim 4, further comprising a cushion ring mountedonto said driving shaft and sandwiched between said cover plate and saidretainer.
 6. The power hand tool as claimed in claim 4, wherein thedriven wheel has a plurality of arched said grooves equiangularly spacedaround a center thereof.